This invention relates to a parallel link robot arm adapted to transport works of comparatively light weight such as semiconductor wafers and IC's without changing posture.
A construction for maintaining a work supporting device provided at an arm end in the same posture, during the arm rotation, has been disclosed in U.S. Pat. No. 3,182,813, in which a chain wheel provided concentrically with the rotating axis of the arm is coupled by chain with the work supporting device provided at the end of the arm.
However, the disclosed construction is operable for transporting works to specific positions along a semicircle by means of a single arm of a comparatively large size, and hence it is difficult to apply such a construction to a parallel link type robot arm which transports works to programmed positions in a plane at a high speed as in the case of securing IC's on, for instance, an IC board.
Another construction to control the attitude and position of a work supporting device by three driving motors, has been disclosed in GB No. 2 060 556A, in which a belt driven by a motor and belts to rotate the work supporting device is connected for controlling the attitude of the work supporting device.
However, in the disclosed construction, the work supporting device can maintain the constant attitude by means of controlling the rotating angle of the motor.